PROJECT SUMMARY/ABSTRACT John E. Greenlee, M.D. Antibodies to intracellular proteins of neurons have been repeatedly demonstrated in serum and cerebrospinal fluid of patients with systemic cancer who develop stereotypic paraneoplastic syndromes of neurological dysfunction. These paraneoplastic neurological syndromes are characterized by destruction of populations of neurons and occur in the absence of tumor metastasis to brain or spinal cord. The role of antineuronal antibodies in the pathogenesis of paraneoplastic neurological injury has remained unclear, since viable neurons have been considered essentially impermeable to IgG. We have studied the interaction of two paraneoplastic autoantibodies, anti-Yo and anti-Hu, with organotypic cultures of rat brains. Anti- Yo, found in patients with cerebellar degeneration in the setting of gynecological and breast cancers, reacts with cytoplasmic proteins of cerebellar Purkinje cells. Anti-Hu antibody, strongly associated with encephalomyelitis in the setting of small cell lung cancer, reacts with nuclear and cytoplasmic antigens found in essentially all neurons. In our studies to date, we have demonstrated that both of these antibodies are taken up by and accumulate within live neurons. Our studies have demonstrated that anti-Yo antibody causes death of Purkinje cells, and that anti-Hu antibody causes death of Purkinje cells as well as other neurons. We have found that Purkinje cells and, to a lesser degree, other neurons can also take up normal IgG. However, normal IgG is readily cleared from neurons and, unlike Yo or anti-Hu antibodies, does not accumulate within neurons over time. Our recent work indicates that uptake of IgG by neurons appears to be dependent upon the Fc portion of the IgG molecule and that Purkinje and other neuronal populations express Fcg receptors. Our proposed work has four goals: 1) To determine whether the ability to incorporate IgG is a universal property of neurons throughout the nervous system; 2) to correlate neuronal Fcg expression with uptake of IgG; 3) to determine whether antibody uptake by neurons is reduced by blockade of Fcg receptors or is absent in knockout mice lacking specific Fcg receptors; and 4) to determine whether other paraneoplastic IgGs are also taken up by neurons and cause cell death;. The proposed research, based on our findings that neurons are able to incorporate antibody, addresses a potential novel mechanism for immune-mediated neurological injury. The studies should be of value in understanding neuronal injury in paraneoplastic and other autoimmune neurological conditions. Information gained from the research should also be of value in understanding the role of antibody-neuron interactions in host defense against infection and in immunotherapy of degenerative neurological diseases.